1. Field of the Invention
This invention relates to radiologic imaging method and apparatus and more particularly to a method and apparatus for reducing the radiation exposure to a subject while maintaining the desired qualities of a conventionally obtained radiograph.
2. Description of the Prior Art
In the past, techniques have been developed for the digital encoding of fluoroscopic images in the digital angiography and for digitalization of the output images of X-ray detectors by computerized axial tomography techniques. These techniques have concentrated on imaging production and have not addressed the problem of reducing the level of radiation exposure to the subject. The need for a reduction in either the radiation dose or noise has been recognized as disclosed at the 6th Conference of the Proceedings of ACR/IEEE Computer Society in 1979 on the computer applications in radiology. The emphasis, however, has been placed on refinements in the X-ray equipment, as for example, the improvements in radiography apparatus as disclosed in U.S. Pat. No. 4,179,100 rather than minimizing the radiation dosage to the subject.
The known approaches to data have centered on image production as opposed to reduction in the radiation exposure other than by reducing the time of exposure and/or the areas of exposure, as disclosed in Med. Physics, Vol. 7, pages 13-18, January/February, 1980, Picture Processing And Digital Filtering by T. S. Huang, 1975 and Digital Image Processing by W. K. Pratt, 1978. In the development of digital radiography systems, the emphasis has been placed on the primary X-ray detector and the image acquisition procedure. This has lead to the development of area detectors, line scan detectors, and point scan or flying spot detectors. All these systems require a two dimensional projection image. PG,4
Typical detector devices for digital X-ray imaging include solid state line scanned systems, large area fluorescent screen-TV camera digital devices and selenium photoconductor area detectors. One of the major impediments to the utilization of digital imaging processing has been the large memory size and long data processing time required. This has hampered the development of digital angiography, digital fluoroscopy, CT and other digital radiography technology. However, by minimizing the X-ray dosage, the problem of large memory size and long data processing time can also be resolved and thereby improve the development of CT, digital angiography, and digital fluoroscopy. This is particularly desirable for these types of systems which are all processed through a digital form.
Therefore, there is need for a digital imaging process that permits reduced radiation exposure in radiological diagnosis by the use of conventional X-ray equipment without a loss in spatial resolution and contrast information. By reducing the radiation dosage, the time for processing the digital information can be accelerated; and the storage space required to process the digital information in the memory system can be substantially reduced.